One of the fastest growing segments of the semiconductor industry is the manufacture of multi-chip modules (MCM). Multi-chip modules are being increasingly used in computers to form PC chip sets and in telecommunication items such as modems and cellular telephones. In addition, consumer electronic products such as watches and calculators typically include multi-chip modules.
With a multi-chip module, non-encapsulated or unpackaged dice (i.e., chips) are secured to a substrate (e.g., printed circuit board) using an adhesive. Electrical connections are then made directly to the bond pads on each die and to electrical leads on the substrate. In general, unpackaged dice cost less to manufacture than the equivalent packaged products. This is because the procedures for packaging semiconductor dice are complex and costly. Substantial cost savings are realized by eliminating packaging procedures.
However, because there is no package, procedures for testing the unpackaged dice are more difficult. With unpackaged dice semiconductor manufacturers are required to supply dice that have been tested and certified as known good die (KGD). Known-good-die (KGD) is a collective term that connotes unpackaged die having the same quality and reliability as the equivalent packaged product. This has led to a need in the art for manufacturing processes suitable for testing bare or unpackaged semiconductor die.
For test and burn-in of an unpackaged dice, a carrier replaces a conventional single chip package in the manufacturing process. The carrier typically includes an interconnect that allows a temporary electrical connection to be made between external test circuitry and the die. In addition, such a carrier must allow the necessary test procedures to be performed without damaging the die. The bond pads on a die are particularly susceptible to damage during the test procedure.
In response to the need for known good die (KGD), semiconductor manufacturers have developed carriers for testing unpackaged die. As an example, carriers for testing unpackaged die are disclosed in U.S. Pat. No. 4,899,107 to Corbett et al. and U.S. Pat. No. 5,302,891 to Wood et al., which are assigned to Micron Technology, Inc. Other test apparatus for unpackaged die are disclosed in U.S. Pat. No. 5,123,850 to Elder et al., and U.S. Pat. No. 5,073,117 to Malhi et al., which are assigned to Texas Instruments.
One of the key design considerations for a carrier is the method for establishing a temporary electrical connection with the bond pads on the die. With some carriers, the die is placed circuitry side down in the carrier and biased into contact with the interconnect. The interconnect contains the contact structure that physically aligns with and contacts the bond pads of the die. Exemplary contact structures include wires, needles, and bumps. The mechanisms for making electrical contact include piercing the native oxide of the bond pad with a sharp point, breaking or burnishing the native oxide with a bump, or moving across the bond pad with a contact adapted to scrub away the oxide. In general, each of these contact structures is adapted to form a low-resistance ohmic contact with the bondpad. Low-resistance refers to a resistance that is negligible. An ohmic contact is one in which voltage appearing across the contact is proportional to current flowing for both directions of flow.
Other design considerations for a carrier include electrical performance over a wide temperature range, thermal management, power and signal distribution, and the cost and reusability of the carrier. In addition, a carrier should be suitable for use with automated equipment and assembly procedures utilized in large scale semiconductor manufacture.
In view of the foregoing, it is an object of the present invention to provide an improved carrier adapted to test and burn-in an unpackaged die without damage to the die. It is a further object of the invention to provide an improved carrier for testing an unpackaged die, that is reusable, that is easy to assemble and disassemble, that provides efficient electrical coupling to contact locations on a die over a wide temperature range, and that can be used for testing different types of dice. It is a still further object of the present invention to provide a carrier useful in the manufacture of known good die that is compatible with automated equipment and processes used in the large scale manufacture of semiconductor dice. Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds.